Year	Number
1970	13.10005
1971	13.63815
1972	12.84415
1973	13.43108
1974	14.36685
1976	16.10254
1981	14.85468
1982	15.66601
1983	15.37848
1986	15.26774
1988	15.10553
1989	14.82182
1990	12.9166
1991	13.19851
1992	13.54265
1993	13.82294
1994	14.0878
1995	14.13826
1996	14.27041
1997	14.39865
1998	14.94995
1999	14.94713
2000	14.57182
2001	14.25666
2002	13.58158
2003	14.23421
2004	14.20076
2005	12.47833
2006	12.26633
2007	13.0443
2008	11.95971
2009	12.59356
2010	12.17648
2011	14.76712
2012	16.61711
2013	15.37529
2014	15.4731
2016	14.11492
2017	15.3284
2018	15.2071